Generally, emulsions of hydrolyzable silanes, such as alkoxysilanes, are difficult to prepare due to hydrolysis and condensation of the alkoxysilanes during the emulsification process and upon aging. Previously, emulsions of hydrolyzable silanes have been prepared by combining the silane with the emulsifiers to form a homogeneous mixture followed by addition of water at very high speeds. Extensive premature hydrolysis of the silane is prevented by controlling the pH near neutral. Alternatively, the emulsifiers were added to the water followed by the silane and homogenization of the mixture.
Wilson, U.S. Pat. No. 4,877,654 (issued Oct. 31, 1989), describes aqueous emulsions useful for rendering porous substrates water repellent comprising (a) a hydrolyzable silane, essentially hydrolytically stable within a determinable pH range, emulsifier(s), and water. The emulsion is prepared by adding the alkoxy silane and emulsifiers to a Waring.RTM. Blender, and then slowly adding water as the speed of mixing is increased. A buffer is added to maintain the pH within a determinable pH stable range. However, the high speeds of a Waring Blender mixer are not practical for large commercial preparations.
Schamberg et al., U.S. Pat. No. 5,091,002 (issued Feb. 25, 1992), describes an aqueous emulsion useful for water-repellent impregnation of porous mineral building materials comprising an emulsion of a mixture of an alkoxysilane and a alkoxypolysiloxane, an emulsifier, and water.
The emulsion is prepared by adding the emulsifiers to the water. The alkoxysilane is then added with stirring and the mixture is homogenized with a gap-type homogenizer. Alternatively, the emulsion is prepared by mixing the silane and the emulsifier with or without an extremely small amount of water, specifically 5-10% by weight of the surfactant, and then adding the total required amount of water.
Von Au et al., U.S. Pat. No. 5,443,627 (issued Aug. 22, 1995) describes emulsions having organopolysiloxane free from basic nitrogen, alkyltrialkoxysilane, an emulsifier and water. The emulsions are prepared by conventional methods for preparing aqueous emulsions. Preferably, some of the water is emulsified with the organopolysiloxane, the alkyltrialkoxysilane and the emulsifier until a viscous oil phase is formed, and subsequently, the remaining water is emulsified again to form a less viscous emulsion.
Suzuki, U.S. Pat. No. 5,226,954 (issued Jul. 13, 1993), describes an aqueous emulsion of a monoalkyltrialkoxysilane and/or condensate thereof, an emulsifier mixture of an anionic emulsifier and a non-ionic emulsifier which are stable for long periods of time and which have excellent waterproofness. The emulsion is prepared by mixing the silane with surfactants and then adding water slowly while stirring at a high rate of greater than 1000 rpm.
Suzuki, U.S. Pat. No. 5,746,810 (issued May 5, 1998), describes an aqueous emulsion of alkylalkoxysilane, water and an emulsifier, which has a stable emulsion state for a long period of time. The emulsion is prepared by emulsifying the alkylalkoxysilane, water, the emulsifier, and optionally, other additives, with an emulsifying and dispersing machine under conditions sufficient to form an emulsion in which droplets of the alkylalkoxysilane in the water has a diameter in the range of from 0.5 to 10 .mu.m.
Chen et al., U.S. Pat. No. 5,393,330 (issued Feb. 28, 1995), describes masonry water repellents comprising aqueous emulsions of alkylalkoxysilanes with either a quaternary ammonium surfactant or a mixture of a quaternary ammonium surfactant with an amino and/or nonionic surfactant. The emulsions are typically prepared by mixing the surfactant(s) with the alkyltrialkoxysilane(s), adding water, and blending.
Chen et al., U.S. Pat. No. 5,686,523 (issued Nov. 11, 1997), describes a stable silane containing composition comprising (I) a water insoluble or slightly soluble alkoxy silane, (II) an emulsifier, (III) water, and (IV) a water dispersible or emulsified polymer containing an alkoxy silane functional group. Precursor silane emulsions are prepared by mixing emulsifier (II) with alkoxy silane (I), adding water (III) and stirring. The precursor alkoxy silane emulsion is added to the reactive dispersion polymer (IV) or to a reactive polymer emulsion comprising (II), (III) and (IV). The method employed to mix these components is not critical and any commonly used low shear equipment is suitable. Mixing may occur before packaging and storage, or immediately before use, as in the case of a two part system.
Osterholtz et al., U.S. Pat. No. 5,714,532 (issued Feb. 3, 1998), describes a stable epoxy silane emulsion and method for preparing the same. The composition comprises (I) a water insoluble or slightly soluble epoxysilane; (II) an emulsifier; (III) water and (IV) a water dispersible polymer containing a functional group with an active hydrogen. Precursor epoxysilane emulsions are prepared by mixing emulsifier (II) with epoxy functional silane (I), adding water (III) to the mixture and stirring. The precursor epoxy silane is then added to the reactive polymer (IV), or to a reactive polymer emulsion which can comprise (II), (III) and (IV). The method employed to mix these component is not critical.